From the author of The Forgotten Plague (1993), which sounded an alarm about the resurgence of tuberculosis, comes another dire warning, this time about the threat of new plagues from emerging viruses. Ryan, a member of both the Royal College of Physicians and the New York Academy of Medicine, painstakingly chronicles numerous outbreaks, including those of hantavirus in the American Southwest in 1993, Ebola virus in Sudan and Zaire in 1976 and in Reston, Va., in 1989, and, of course, HIV. In addition to recounting the grim details, he examines the circumstances under which these new, lethal viruses have emerged and proposes an intriguing explanation of what is going on. Ryan's theory is that viruses have co-evolved with their feral hosts, with which they have developed a symbiotic relationship. When a rival species, such as humankind, intrudes on the host's environment, the virus attacks the invader. Vast numbers of viruses exist in the rainforests of the world, as well as in the grasslands and the oceans, and as deforestation, agricultural intrusion, and coastal pollution continue, humans can expect to encounter them. As yet, no new virus has been both lethal and highly infectious; however, if one were to emerge that combined these two characteristics--as deadly, say, as HIV and as contagious as the common cold--the result could be a pandemic of catastrophic proportions. He urges increased international cooperation to reduce abuse of the environment, and he calls on governments and the medical profession to get ready now for the very real danger posed by a new viral pandemic. Detailed, Berton Rouechâ€š-style accounts of medical detection in support of a powerful doomsday warning.